This invention relates to paper registers for printing presses and more particularly, to a unique control structure for such paper registers.
Paper registers are employed in conjunction with a wide variety of printing presses. These devices are required to insure that individual sheets of paper are properly aligned or in register prior to entering the printing press. Proper register is critical to the printing operation. In the area of multicolor printing, such as that accomplished with offset presses, the individual sheet is often run through the printer a plurality of times. Therefore, it must be in exact register during each step of the color printing in order to insure proper overlay of the colors. Also, exact register is a must when printing business forms where several sheets are to be employed.
Present registers generally include a plurality of forward or head stops positioned just upstream of the printer and a pair of side guide blocks or side registers. The head stops and side guide blocks are adjustable to place the sheets in proper register prior to entry into the printer. In a typical press, an automatic paper feed will pick up a single sheet of paper and feed it into the register. The register includes one or more belt-type drive elements which feed the paper in a forward direction until it abuts the head stops. The head stops locate the paper in the direction of movement. The paper's forward movement is then stopped and one of the side guides will automatically shift laterally to place the paper in proper position or register cross-wise of the direction of movement. In order to prevent wrinkling, buckling, or skewing of the paper during the shifting phase of the registration process, one or more paper control devices are employed. These control devices exert a downward pressure on the paper to prevent buckling which may result from the paper lifting off the feed bed of the register.
The paper controls have taken various forms including that of metal straps. These straps require adjustment in order to accommodate and exert the proper pressure for the particular size, weight and thickness of the paper employed. Further, these metal straps have a tendency to produce static electricity which may result in improper paper registration or wrinkling of the paper. Also, wheel arrangements have been employed. These wheels similarly require adjustment for the various weights of paper employed. The adjustments necessary for proper operation are time consuming and the controls themselves limit the maximum feed rates obtainable. The wheels also have an adverse effect upon side guide register operation which again reduces or limits feed rates.
In prior registers, "end bounce" has reduced feed rates. This end bounce is caused by the paper hitting the head stops and in effect bouncing back resulting in buckling or wrinkling. Further, since sheets may vary in size even within the same shipping case, "back trim" has been a substantial problem in the industry. When register is controlled by wheels on the back of the feed mechanism, the sheets must be trimmed to the same exact size (back trimmed) for proper register.
The problems experienced with proper adjustment of the control devices are further aggravated by the fact that the paper may vary in thickness within the tolerances specified for a nominal paper thickness. As a result of this variance, the pressure exerted on a paper by the metal straps or the wheel arrangements may vary during operation and can result in wrinkling of the paper. In an attempt to alleviate this problem, a control device in the form of a carrier having a plurality of holes has been employed. A plurality of equal weight and equal diameter spherical pressure elements or balls, such as marbles, are arranged in tandem within the holes. The carrier is mounted over the feed bed and the spherical pressure elements are permitted to float in a vertical direction to compensate for the thickness variation in the paper stock. Also, since the marbles will rotate universally, resistance to sidewise shifting of the paper in the register is reduced which in turn reduces the occurrence of wrinkling. Although this form of paper control device is superior in performance to the metal strap and wheel structures, such ball type devices exert the same pressure along their lengths regardless of the thickness or weight of paper employed. As a result, the maximum feed rates obtainable will vary with the particular type of paper used.
Another factor significantly affecting the rate at which paper can be fed to a press using conventional control devices is humidity. Changes in humidity require adjustment of the register control devices and changes in the feed rate or both. Both of these requirements reduce the productive capacity of the press.